Dielectric containing halogenated aromatic hydrocarbon and mono ortho tolyl biguanide as corrosion inhibitor



Feb. 3, 1953 E. E. HARDY 2,627,504

DIELECTRIC CONTAINING HALOGENATED AROMATIC HYDROCARBON AND MONO ORTHO TOLYL BIGUANIDE AS CORROSION INHIBITOR Filed July 14. 1948 FIG.2

1/4/1111 III/11114 DIELECTRIC METAL CONTAINING CHLORINAT'ED ELECTRODES 4 BIPHENYL AND MONO-ORTHO TOLYL BIGUANIDE AS CORROSION INHIBITOR FIG. 4

PAPER IMPREGNATED WITH CHLORINATED BIPHENYL AND MONO-ORTHO-TOLYL BIGUANIDE A5 CORROSION INHIBITOR FIG. 3

INVENTOR. Edgar E.Hurdy ATTORNEY Patented Feb. 3, 1953 DIELECTRIC CONTAINING HALOGENATED AROMATIC HYDROCARBON AND MONO ORTHO TOLYL BIGUANIDE AS CORRO- SION INHIBITOR Edgar E. Hardy, Anniston, Ala., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware Application July 14, 1948, Serial No. 38,733

6 Claims.

The present invention relates to novel compositions of matter comprising halogenated organic compounds and a scavenging or corrosion-inhibiting material selected from the group consisting of biguanide and its substituted derivatives. More specifically the invention relates to apparatus, particularly electrical apparatus such as capacitors, transformers, circuit breakers, cables and the like containing the above compositions.

I-Ialogenated organic compounds, more particularly halogenated aromatic compounds such as chlorinated biphenyl and chlorinated naphthalene are highly useful electrical insulating and heat exchanging materials because of their high dielectric constants, thermal stability, resistance to oxidation, non-flammability and other valuable properties. However, it has been found that when exposed to elevated temperatures and/or high voltages, they partially decompose liberating hydrogen halides which are exceedingly corrosive to heat exchanging equipment and electrical apparatus.

For example, in transformers, circuit breakers and other electrical devices in which arcing occurs, the development of hydrogen halides as a result of the above decomposition presents a serious problem as they decrease the dielectric strength of the composition containing same and cause considerable damage by attacking paper insulation and corroding metal parts of the apparatus in which the composition is used. The undesirable effect of the above decomposition is further manifested when the above halogenated organic compounds are used as capacitor impregnants. Thus, under high operating temperatures and direct current voltages, capacitors impregnated therewith undergo a characteristic type of deterioration which results in an ever increasing leakage current, a short capacitor life, visible localized decomposition of the dielectric and corrosion of the electrodes. Moreover, in the case of capacitors operating on alternating current, the decomposition sometimes results in an excessive increase in power factor of the dielectric material.

It is, therefore, the object of the present invention to provide new compositions of matter containing halogenated organic compounds wherein the above objectionable properties are either completely eliminated or substantially reduced.

An additional object is to provide transformers, capacitors, circuit breakers, cables and the like containing halogenated organic compounds in combination with a corrosion inhibitor or scavenger whereby the deleterious action of hydrogen halides on the paper insulation and metal 2 parts thereof is eliminated or materially reduced.

Another object is to provide a capacitor impregnant containing halogenated organic compounds and a corrosion inhibitor or scavenger whereby the deleterious eiTect of hydrogen halides on the electrodes and paper insulation of capacitors is substantially reduced or completely eliminated with the result that the capacitor has a longer useful life and greater dielectric stability than similar capacitors not containing the corrosion inhibitor.

A further object is to provide the cellulosic insulation in transformers containing liquid halogenated organic compounds with protection against rapid destruction by hydrogen halides evolved as the result of a minor are within the transformer, thus permitting complete repair of the assembly by rapid replacement or removal of the particular part that gave rise to the arc and thereby avoiding destruction of the entire paper insulation of the transformer with a consequent high cost of repair.

A still further object is to provide switches, cables and the like containing halogenated organic compounds and a corrosion inhibitor or scavenger which practically eliminates the rusting and corrosion normally accompanying the use of such devices filled with halogenated organic compounds per se.

Other objects and advantages of the present invention will become apparent to those skilled in the art as the description proceeds.

I have discovered that halogen decomposition products can be rendered substantially innocuous and the above objectives accomplished if, in accordance with the present invention, the halogenated organic compound to be protected is associated with at least one compound selected from the group consisting of biguanide and its substituted derivatives. Such compounds may be represented generically by the following structural formula:

wherein R1, R2, R3 and R4 may be hydrogen, alkyl, aryl, aralkyl and alicyclic hydrocarbon radicals. Specific examples of compounds of For a more complete understanding of the present invention, reference is made to the accompanying drawings and the experimental data.

hereinafter presented in the specific examples.

Figure 1 is a front elevation partly in section of a transformer; Figure 2 illustrates a switch in a similar manner; Figure 3 represents a rolled capacitor; Figure 4 shows a sectional view of a portion of the electrodes and dielectric sheets of Figure 3; and Figure 5 is a side view of a cable, the casing being partly removed to permit the interior of the parts to be seen.

The transformer illustrated in Figure 1 comprises a casing I, core 2, coils 3 insulated with manila paper, kraft' paper, cotton or other fibrous insulation, insulating and cooling medium 4, lead-in bushings 5, and suitable leads 6 connected "to the coil assembly. The insulating and cooling medium may consist of chlorinated biphenyl, trichlorbenzene and mono ortho tolyl biguanide in the following proportions.

Parts by weight Chlorinated biphenyl (60% Cl) 60 Trichlorbenzene 40 Mono ortho tolyl biguanide 0.1

deleterious effect of such liquid on organic insulation but will also greatly reduce the corrosion of the metal parts of the transformer which come in contact therewith in the presence or absence of air.

The switch shown in Figure 2 comprises a casing 6', fixed contacts I and 8, and movable contactsa and II! which cooperate therewith. The

movable contacts are mounted upon a support i i which in turn is operatively connected to actuating levers l2. The following is illustrative of a suitable arc quenching liquid which may be used in this device, it being understood that the invention is not limited thereto.

Parts by Weight Chlorinated biphenyl (55% C1) 80 Trichlorbenzene 20 Mono ortho diphenyl biguanide 0.05

In the operation of electric switches, the unavoidable arcing which accompanies make-andbreak of the switch contacts results in partial decomposition of the chlorinated biphenyl or other halogenated organic compounds. The

' presence of the biguanides of the present inven- -panying the use of such devices filled with halogenated organic compounds per se.

The capacitor shown in Figure 3 is made up of alternate layers of metal foil such as aluminum or tin foil separated by sheets of dielectric material. It is produced by interleaving two dielectric sheets, such as linen or kraft paper, with the metal foil, and rolling the interleaved sheets in the conventional manner. The rolled capacitor is then impregnated with the dielectric composition by any suitable process, such as vacuum impregnation, with chlorinated biphenyl having dissolved therein a small proportion of a biguanide such as mono xylyl biguanide. The capacitor is then placed in a protective case or otherwise used as desired.

The following range of compositions is illustrative of suitable capacitor impregnants:

COMPOSITION I Liquid chlorinated biphenyl, particularly chlorinated biphenyl containing from 42% to 60% by weight of chlorine, 0%-about by weight Conventional chlorinated organic dielectric materials as disclosed herein, about 100 %-O% by weight Bi uanide or substituted derivatives, 0.0l%-l% by Weight COMPOSITION II Parts by weight Chlorinated biphenyl (42%60% Cl) 60 Trichlorbenzene 40 Mono ortho tolyl biguanide 0.1

Of the above range of compositions, th preferred capacitor impregnant is one having the following compositions:

Parts by weight Chlorinated biphenyl (60% Cl) 60 Trichlorbenzene 40 Mono ortho tolyl biguanide 0.1

The presence of biguanides in chlorinated biphenyl or other halogenated organic compounds provides excellent protection against the deleterious action of halogen decomposition products on metal, paper and other organic insulation material and consequently capacitors provided there- With will have a longer useful life and greater dielectric stability than similar capacitors containing halogenated organic compounds per se. Moreover, capacitors containing biguanides will not exhibit an ever increasing power factor with time when operated at high temperatures and voltages as is typical of capacitors impregnated with halogenated organic materials which are not associated with one of the above corrosion inhibitors.

Figure 4 shows a section of one turn of the finished rolled capacitor illustrating the alternate electrodes and dielectric layers. In accordance with the present invention, the finished capacitor contains a halogenated organic compound, preferably chlorinated biphenyl, and a minor portion of biguanide or its substituted derivatives.

The cable of Figure 5 comprises a core [3, cable conductors i i, insulation consisting of paper or other suitable material i5 and a casing It. The space between the insulated conductors and the casing is filled with a mixture of any of the liquid chlorinated organic compounds and biguanides mentioned above. Such a composition may consist of a mixture of the followin ingredients, but it is to be clearly understood that the invention is not restricted thereof.

Parts by weight Chlorinated biphenyl (60% Cl) 50 Trichlorbenzene 50 Menu xylyl biguanide 0.1

In addition to the applications mentioned above, the compositions of the present invention are useful as heat exchange media for controlling the temperature of catalytic and other chemical reactors, for cooling gases and liquids and for use in numerous other heat exchanging operations.

The experimental data hereinafter presented illustrate in a striking manner the scavenging or corrosion inhibiting action of biguanides on dielectric compositions containing halogenated organic compounds. In accordance therewith, the effect of the corrosion inhibitor is brought out by showing and comparing the action of an I-iClsaturated halogenated dielectric composition, with and without the inhibitor, on organic dielectric materials such as paper. The effectiveness of the inhibitor is manifested by the protec tion it affords paper against attack by hydrogen chloride and the degree of attack is indicated by the extent to which the tensile strength of the paper is decreased. This will be rendered more apparent by reference to the following examples.

Example I Six strips of manila wrapping paper (6 x 1") were humidified at 65% R. H. at 70 F. for a period of 48 hours and subjected to tensile strength tests. These tests were run on a Scott IP2 serigraph with a jaw separation of 3 inches and a rate of travel of 34.5 seconds for a load of 40 lbs. The result of these tests, being the average of 6 breaks, was as follows:

Tensile strength of paper samples, 46.2 lbs/in.

Example II Six strips of the same piece of manila wrapping paper (7" x 1") were allowed to soak at a temperature of 75 C. for 1 hours in an HCl saturated solution consisting of 60 parts by weight of chlorinated biphenyl (60% Cl) and. 40 parts by weight of trichlorbenzene and at the end of this operation, the papers were soaked for minutes in benzene, another 15 minutes in methanol and dried. After cutting one-half inch from each end of the dried paper strips, they were subjected to the above tensile strength tests with the following result:

Tensile strength of impregnated paper samples, 11.5 lbs/in.

These examples demonstrate that HCl had et highly deleterious action on the samples since the tensile strength of the paper changed from 46.2 lbs/in. to 11.5 lbs./in., a decrease in tensile strength of approximately 75%.

Example III The foregoing example was repeated using samples of the same paper and the same impregnant except that 0.1 part by weight of monoortho tolyl biguanide was added. The tensile strength of the impregnated paper was found to be 45.3 lbs./in., thus demonstrating that the above compound is a highly effective material for 6 rendering halogen decomposition products such as HCl innocuous to paper or other fibrous organic dielectrics.

Example IV The procedure described in Example III was followed except that mono ortho biphenyl biguanide in an amount corresponding to 0.1 part by weight was substituted for mono ortho tolyl biguanide. The paper samples had an average tensile strength of 20 lbs/in. as compared with 11.5 lbs/in. for the samples treated with impregnant not containing a scavenger, and 46.2 lbs/in. for the unimpregnated samples.

This example shows that mono ortho biphenyl biguanide is less effective than ortho tolyl biguanide; however, it is still a highly satisfactory scavenger or corrosion inhibitor for halogenated organic compounds as it is superior to tetraphenyl tin, a material used commercially for the above purpose. As evidence of its superiority over tetraphenyl tin, reference is made to the following results of tensile strength tests made with both of these compounds:

Lbs/in.

Tensile strength of untreated paper 46.2 Tensile strength of paper treated with composition consisting of 60 parts by weight of chlorinated biphenyl (60% Cl) 40 parts by weight of trichlorbenzene and 0.1 part by weight of tetraphenyl tin Tensile strength of paper treated with composition consisting of 60 parts by weight of chlorinated biphenyl (60% Cl), 40 parts by weight of trichlorbenzene and 0.1 part by weight of mono ortho biphenyl biguanide 20 These tests show that the average tensile strength of the paper samples was reduced from 46.2 lbs./in. to 16 lbs/in. in the case of tetraphenyl tin whereas when mono ortho biphenyl biguanide was employed, the tensile strength was reduced only to 20 lbs./in., thus demonstrating the superior scavenging action of the latter compound.

The following ta'ble illustrates the electric properties of the dielectric composition consisting of 60 parts by weight of chlorinated biphenyl (60% Cl) and 40 parts by weight of trichlorbenzene and also shows the effect thereon of adding 0.1 part by weight of mono ortho tolyl biguanide and mono ortho biphenyl biguanide.

The above experimental data indicate that the above biguanides do not seriously affect but actually improve the electrical properties of the halogenated organic compounds associated therewith and that, therefore, such compositions are suitable for use in transformers, capacitors, switches, cables and other electrical devices.

f The description of the present invention. has been directed primarily to compositions containing chlorinated biphenyl, trichlorbenzene and. biguanide or its substituted derivatives, but it is to be understood that the invention is not restricted thereto but embraces halogenated organic compounds generally. Thus, the above biguanides may be used as stabilizers, scavengers or corrosion inhibitors for chlorinated naphthalene, chlorinated diphenyl ketone, chlorinated diphenyl oxide, chlorinated diphenyl methane, chlorinated diphenyl ethane, chlorinated benzene, chlorinated toluene, chlorinated nitro diphenyl, chlorinated alkylated benzenes, chlorinated alkylated biphenyls, ethyl trichlorbenzene, ethyl tetrachlorbenzene, ethyl pentachlorbenzene, chlorinated terphenyls, chlorinated quaterphenyls, chlorinated parafiinic hydrocarbons, chlorinated alicyclic hydrocarbons, chlorinated oxygen-containing organic compounds, chlorinated rubber, chlorobutadiene polymers, polyvinyl chloride, polymeric vinyl chloroacetate, chlorinated fats, chlorinated vegetable oils, chlorinated animal oils, chlorinated mineral oils or mixtures of two or more of these. In place of the chlorinated compounds, the corresponding fluorine, bromine and iodine derivatives may be used. In fact, any halogenated organic compound or composition which tends by reason of its halogen content to cause corrosion of metals or dehydration of paper or organic fibrous insulation, may be rendered substantially innocuous by means of the biguanides defined by the general formula set out above.

The method of incorporating the biguanides varies with the halogenated organic compound or composition. If the compound or composition is liquid at room temperature, the above compounds are merely dissolved therein in suitable concentrations; if it is a solid, the biguanides are blended therewith by the use of solvents or swelling agents or by means of mixing rolls, etc.

In the case of halogenated polymers, the biguanides may be incorporated before, during or after polymerization of the corresponding monomers.

The quantity of biguanides used varies with the halogenated organic compound or composition. In general, satisfactory results are obtained by employing these compounds in an amount varying from 0.05% to 1% and preferably from 0.05% to 0.1% by Weight of the halogenated organic compound or composition, but it is to be understood that the invention is not limited thereto as slightly lower and somewhat higher concentrations may be employed. Stated broadly, the biguanides may be used in amounts varying from 0.01% by weight. up to and above the limit of their solubility in the halogenated organic compound or composition. In most instances, it is desirable not to exceed the solubility limits of the biguanides, but there are some applications such as heat exchanging operations in which this may be done without harmful effects.

As widely different embodiments of this invention may be made without departing from the spirit thereof, it is to be understood that the invention is not limited to the specific embodiments except as defined in the appended claims.

What I claim is:

1. A heat transfer and dielectric composition consisting essentially of chlorinated biphenyl and from about 0.05% to about 1% by weight of mono ortho tolyl biguanide.

2. An insulating and cooling composition for electric apparatus consisting essentially of a liquid chlorinated biphenyl and from about 0.05% to about 0.1% by weight of mono-ortho tolyl biguanide, said chlorinated biphenyl containing from 42% to by weight of chlorine.

3. A heat transfer and dielectric composition consisting essentially of chlorinated biphenyl, trichlorbenzene and from about 0.05% to about 1% by weight of mono-ortho tolyl biguanide.

4. A dielectric composition consisting essentially of chlorinated biphenyl and from about 0.05% to about 1 by weight of mono ortho tolyl biguanide, said chlorinated biphenyl containing 60% by weight of chlorine.

5. A dielectric composition consisting essentially of chlorinated biphenyl, trichlorbenzene and about 0.05% to about 0.1 by weight of mono ortho-tolyl biguanide.

6. A dielectric composition consisting essentially of about 60% by weight of chlorinated biphenyl, about 40% by weight of trichlorbenzene and about 0.1% by weight of mono ortho tolyl biguanide, said chlorinated biphenyl containing about. 60% by weight of chlorine.

EDGAR E. HARDY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,041,594 Clark May 19, 1936 2,043,257 Missbach June 9, 1936 2,069,711. Missbach Feb. 2, 1937 2,077,429 McMahon a Apr. 20, 1937 2,125,381 Levine Aug. 2, 1938 2,339,091 McLean Jan. 11, 1944 2,468,544 Clark a Apr. 26, 1949 

1. A HEAT TRANSFER AND DIELECTRIC COMPOSITION CONSISTING ESSENTIALLY OF CHLORINATED BIPHENYL AND FROM ABOUT 0.05% TO ABOVE 1% BY WEIGHT OF MONO ORTHO TOLYL BIGUANIDE. 